With the advent of air pollution control requirements, it has been necessary to remove sulfur dioxide from effluent gases that had previously been expelled into the atmosphere. The further processing of the so-accumulated sulfur dioxide is a practical necessity, and accordingly, various systems have been proposed for converting the sulfur dioxide to sulfur, such as by using natural gas or some other relatively expensive reducing agent. In accordance with the present invention, however, high sulfur coal can be used as the reducing agent. This enables the obtainment of a two-fold advantage, in that coal is much less expensive than natural gas and other reducing agents, and also in that a use can be provided for the high sulfur coal which no longer is in demand for power plant use in view of the more stringent air pollution requirements that have been promulgated. A significant advantage afforded by the instant invention lies in the ability to carry out the reduction of sulfur dioxide with low volatility coal at much lower temperatures than heretofore had been possible or even thought to be possible. Thus, in accordance with the present invention, sulfur dioxide, which is normally considered a pollutant, can be used to economically produce a useful product, such as sulfur.